This invention relates to a process for hydrogenating conjugated diene polymers and more particularly, to the process for hydrogenating the unsaturated double bonds of the diene units of conjugated diene polymer, wherein the unsaturated double bonds of conjugated diene polymers, which has been widely used as a modifier for transparent impact-resistant resin or polyolefin and polystyrene resin, is saturated via hydrogenation in the presence of a novel homogeneous catalyst of the organotitanium in the absence of a separate reducing agent, thus representing a high hydrogenation yield with a good reaction reproducibility.
Some polymers of conjugated diene such as 1,3-butadiene or isoprene, have been widely applicable as an elastomer in the industrial field, together with copolymers formulated by these conjugated dienes and copolymerization-possible aromatic vinyl monomers(e.g., styrene, etc.). Since these polymers have a double bonds within their internal chain, their vulcanization is made available but with poor durability and poor resistance to oxidation.
The conjugated diene-aromatic vinyl monomer block copolymers which are not vulcanized, have been as thermoplastic elastomer used for a transparent impact-resistant resin, or for a modifier for polyolefin and polystyrene resin. However, the double bonds in these copolymers are concerned directly with poor durability and poor resistance against oxygen and ozone in the air.
Under such situation, these copolymers need to be used within limited scope of application, while not being exposed to the external environment.
To overcome the shortcomings as aforementioned, a method designed to improve the durability and oxidative resistance of these polymers is to hydrogenate the internal double bonds for saturation in part or whole.
In polymers with the olefinical double bonds, the method of adding hydrogen to the internal double bonds is generally classified into the following two types: (a)a method of using heterogeneous catalysts, and (b)a method of using homogeneous catalyst belonging to Ziegler type catalyst or the organometallic compounds such as Rh and Ti.
According to the hydrogenation of using the heterogeneous catalyst, the olefinic polymers are dissolved in an appropriate solvent and then, contacted with hydrogen in the presence of a heterogeneous catalyst. However, shch method has recognized some disadvantages in that (a) due to adverse factors such as steric hindrance of polymers and relatively high viscosity, the contact may not be easily made between the reactant and catalyst, and (b) if hydrogenation is successfully achieved due to strong adsorption of both the polymer and catalyst, their not easily detachable bonding characteristics make other unhydrogenated polymers extremely difficult to reach the activated point.
The complete addition of hydrogen to the double bonds in the case of the heterogeneous catalyst should require a large volume of catalyst including severe conditions such as high temperature and high pressure, which may result in degradation of polymer and gelation as well. In particular, in case of copolymers comprising conjugated dienes and aromatic vinyl mononers, the saturation of the double bonds in an aromatic compound is simultaneously performed, which makes it difficult to selectively hydrogenate the double bonds of olefinic polymer only.
In addition, physical separation of the residual catalyst from the resulting polymer solution after hydrogenation would be extremely difficult, and a part of heterogeneous catalyst is strongly absorbed to the polymer, whereby its removal is not completely made available.
In contrast to the hydrogenation of using heterogeneous system catalyst, a hydrogenation designed to use a homogeneous catalyst is characterized in that (a) catalytic activity is high, and (b) with less amounts of catalyst, hydrogenation can be made available with higher yield under a mild conditions, i.e., low-temperature and low-pressure.
On top of that, if the homogeneous catalyst is used, its advantage is to selectively hydrogenate the olefinic double bonds only among the chains of copolymer consisting of aromatic vinyl hydrocarbon and conjugated dienes under appropriate hydrogenation conditions.
Notwithstanding this, hydrogenation of the unsaturated double bonds using the homogeneous catalyst is responsible for lowering the stability of catalyst itself, and the separation of the deactivated catalyst from hydrogenated polymers becomes extremely difficult.
Meantime, several hydrogenations or selective hydrogenation involved in the conjugated diene polymers were disclosed in the prior arts. For example, in order to hydrogenate or selectively hydrogenate the polymer containing an ethylenically unsaturated double bonds, or the polymer having aromatic and ethylenically unsaturated double bonds, the methods of using appropriate catalysts published in the prior arts, preferably some catalysts containing 8-, 9- and 10-group metals or precursor of catalysts, were disclosed in the U.S. Pat. No. 3,494,942, No. 3,634,594, No. 3,670,054, and No. 3,700,633.
According to these methods, the catalyst includes 9- and 10-group metals, especially some catalyst prepared by nickel or cobalt compounds in combination with an appropriate reducing agent such as alkyl aluminium. The prior arts disclosed that in addition to alkyl aluminium, 1-, 2- and 13-group metals in the Periodic Table of the Elements, especially lithium, magnesium and aluminium alkyl or hydride, might be used as an effective reducing agent. In general, the blending ratio of both 1-, 2- and 13-group metals and 8-, 9- and 10-group metals is in the molar ratio of 0.1:1 to 20:1, preferably in the molar ratio of 1:1 to 10:1.
The U.S. Pat. No. 4,501,857 has also disclosed that via hydrogenation of conjugated diene polymer in the presence of one bis(cyclopentadienyl)titanium compound at least and one hydrocarbon lithium compound at least, the double bonds within the polymer may be selectively hydrogenated.
Further, the U.S. Pat. No. 4,980,421 has also disclosed that pseudo-hydrogenation activity may develop via combination of alkoxy lithium compound with bis(cyclopentadienyl) titanium compound, which may be directly added or as a mixed form of organolithium compound and alcoholic or phenolic compound. This invention has reported that the catalytic activity was quite effective even less catalyst used and the residual amount of catalyst did not reversely affect the stability of hydrogenated polymer formed after hydrogenation Another hydrogenation process using bis(cyclopentadienyl)titanium diaryl compound as bis(cyclopentadienyl)titanium compound was disclosed in the U.S. Pat. No. 4,673,714. According to this invention, the unsaturated double bonds of conjugated diene were hydrogenated in the absence of hydrocarbon lithium compound.
Further, there was another process of hydrogenating a conjugated diene polymer including generation of a living polymer via polymerization or copolymerization of conjugated diene monomer as an initiator of organo-alkalimetal polymerization in the presence of an appropriate solvent, which was disclosed in the U.S. Pat. No. 5,039,755. According to this invention, the polymerization of the living polymer, so formed, is terminated with the addition of hydrogen. From a conjugated diene unit of terminated polymer, the selective hydrogenation of the double bonds was carried out via a catalyst expressed by (C.sub.5 H.sub.5).sub.2 TiR.sub.2 (wherein R is a arylalkyl group).
Another method of hydrogenating the double bonds of conjugated diene was disclosed in the U.S. Pat. No. 5,583,185 via use of a catalyst represented by (C.sub.5 H.sub.5).sub.2 Ti(PhOR).sub.2 or (C.sub.5 H.sub.5).sub.2 TiR.sub.2 as a homogeneous system catalyst.
However, the hydrogenation activity of such homogeneous system catalysts differs greatly depending on the reduced state of catalyst and then, the reproducibility of hydrogenation may be lowered. Thus, a high-yield hydrogenated polymer with high reproducibility cannot be easily obtained.
Further, when the reaction is being carried out, there is a trend that some active ingredients of catalyst is contaminated into the inactive ones by the impurities. This is liable to lower the hydrogenation activity which may result in poor reaction reproducibility.
In the homogeneous catalyst, the hydrogenation yield is significantly affected by the stability of catalyst during the hydrogenation process.
Therefore, hydrogenation of a polymer based on the homogeneous catalyst has encountered a lot of problems, when applied to the industrial scale.
Under such situation, the implementation of more economical hydrogenation process should require more effective, high-active and stable catalyst with less amount than the conventional homogeneous system catalysts. Further, a novel catalyst needs to be made available so as to avoid any complicated process to remove catalyst residues from the hydrogenated polymer after reaction.